I read an interesting analysis of sex ratios at birth by Christophe Guilmoto.

As sex identification technology spread through Asia, sex-selective abortion has followed, allowing for greater expression of son preference, and a skewed ratio of boys to girls. The biological average is about 105 boys for every 100 girls, and the most extreme deviation from that now is found in China and Azerbaijan, with ratios of 120:100.

China’s run-up in sex ratios follows a long evolution that saw a decline in female infanticide after the 1950s, followed by a retrenched son preference under the combination of the one-child policy and the collapse of the social welfare system — and enabled by increased access to ultrasound technology.

However, South Korea is a country that apparently reversed course, dropping from over 115:100 in the mid-1990s to near-normal now:

Guilmoto attributes South Korea’s improvement to increased educational and job opportunities for women, made possible by economic development, and anti-discrimination legislation.

He also has some interesting speculation, especially about the effect of a bubble of “surplus” men — many of whom will not be able to marry:

In such a greatly altered demographic environment, having a son who may never marry would soon represent a serious social or economic hazard. It is ironic that the very precepts that underlay the initial demand for sons (and the parallel aversion to daughters) would deal a fatal blow to the patriarchal system.